Develop radiopharmaceuticals for the quantification of regional coronary blood flow. When developed, these agents will be tested in dogs, and ultimately, in man. The compound with the hightest priority is Iodine-123 hexadecenoic acid (palmitic acid, a fatty acid) which behaves like a potassium analogue. Problems still exist in its production. It has a very short half-life in myocardium; thus, limiting the study (one view only possible). Therefore, longer chain fatty acids are also being considered, especially those with greater than 20 carbons. Other compounds are mentioned for study, such as two fluortetradecenoic acid and its analogues.